The present invention relates to sintered metal bodies, particularly bodies of annular configuration suitable for use as the seat of a ball valve, whose pores or interparticulate spaces are impregnated with a polymeric material such as PTFE or TFE (Teflon).
It is desirable to use metal seats in a ball valve under certain circumstances since the resultant valve configuration can resist higher pressures than valves which use other types of seat materials, e.g., PTFE seats. When a metal seat is disposed adjacent a ball, however, there is considerable friction between the two which could cause galling problems, and therefore, in an effort to reduce these friction problems somewhat, it is typical for metal seats to be used in conjunction with trunnioned ball valves so that the pressure between the ball and seat can be carefully controlled due to the fact that the ball is mounted for rotation on its own trunnion. This, however, is a comparatively expensive construction. Metal seats are hardly ever used in floating ball arrangements due to the high torques which would result, the galling problems, etc.
McFarland et al U.S. Pat. No. 3,592,440, the disclosure of which is incorporated herein by reference inasmuch as the patent discloses manufacturing techniques and materials suitable for use in the improvement of the present invention, seeks to avoid some of these problems, and to provide a metal seat capable of use in a floating type ball valve, by providing a sintered metal seat whose exterior surfaces are coated with a layer of cured polymeric material, e.g., PTFE, and whose interior pores or interstices are partially filled with cured polymeric material. The seat of the McFarland et al patent is, however, a porous structure which relies upon a continuous surface coating of polymeric material to achieve a desired seal, or upon a caulking action of the polymer increments within the seat to effect a desired seal in the event that the surface polymer coating should be destroyed by fire or abrasion. This known seat, being essentially porous throughout, will therefore tend to leak fluid through the seat when the seat is subjected to pressure if the integrity of the surface coating should be impaired and the aforementioned caulking effect is imperfect.